JP2019117423A - Image capturing optical system and image capturing device - Google Patents

Abstract

To provide an optical system which has a simple and compact configuration that offers a large image circle.SOLUTION: An image capturing optical system 10 comprises a first lens group G1 having positive refractive power as a whole, a second lens group G2 having negative refractive power as a whole, an aperture stop St, and a third lens group G3 having positive refractive power as a whole, arranged in order from the object side 11 toward an image plane 5a, and is configured such that the second lens group moves while focusing. The third lens G3 consists of an aperture stop-side lens L7 with positive refractive power disposed on the most object side 11, a lens L8 with positive refractive power, a biconcave negative lens L9, and an image plane-side lens L10 with negative refractive power disposed on the most image plane side 12.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical system for imaging suitable for an imaging device such as a camera.

  Patent Document 1 shows an inner focus type lens in which the second lens group is moved as one unit at the time of focusing with a configuration of positive, negative and positive 3 groups 8 to 9 from the object side, and the predetermined lens configuration and conditions By satisfying the equation, it is described to obtain a compact lens well corrected for aberration, which is suitable for a camera with a large film size. Specifically, from the object side, a positive second lens group consisting of two positive lenses, a negative lens, and a positive lens in order from the object side, and a negative second lens consisting of a negative lens and a positive lens and moving integrally at the time of focusing A lens is disclosed in which a fixed and positive third lens group consisting of a group, a positive lens, a negative lens, and a positive lens is arranged.

JP 2002-107616 A

  A large image pickup element is being adopted for an image pickup apparatus such as a camera, and a lens system (optical system) for image pickup having a large image circle corresponding thereto is demanded. In an optical system having a large image circle, in particular, an optical system having a large angle of view, the lens size becomes large and the back focus tends to be relatively short. For this reason, there is a demand for realizing an optical system with a large image circle in a compact configuration with a simple configuration.

  One of the aspects of the present invention is, in order from the object side to the image plane, a first lens group of generally positive refractive power, a second lens group of generally negative refractive power, and an aperture stop And a third lens group having a positive refractive power as a whole. This optical system is an inner focus type in which the first lens group, the aperture stop, and the third lens group are fixed with respect to the image plane and the second lens group moves with respect to the image plane during focusing. The third lens unit includes a lens having a positive refractive power, which is disposed closest to the object, a lens having a positive refractive power, a negative biconcave lens, and a negative that is disposed closest to the image surface. And an image-side lens of a refractive power of By disposing two negative power lenses on the image plane side of the third lens group, it is possible to provide an optical system having a large image circle with respect to the back focus BF. By making the surface on the image surface side of the second negative lens from the image surface concave on the image surface side, it is possible to suppress an increase in the angle of light incident on the image surface, and a clearer image is formed. It can be an image.

The distance dS between the object-side surface of the stop lens and the aperture stop and the distance dI between the surface of the stop lens and the image plane may satisfy the following condition (1).
0.02 <dS / dI <0.3 (1)

  This optical system as a whole has a power distribution close to a positive-negative-positive telephoto type (telephoto type), and is a type that can easily ensure a relatively long back focus. On the other hand, as in the lens system shown in Document 1, the lens diameter on the object side tends to be larger than the lens diameter on the image plane side. For this reason, if the lens diameter on the image plane side is increased in order to enlarge the image circle, the lens diameter on the object side is further increased, and it is difficult to design the optical system compact. In addition, when the lens diameter on the object side is reduced, the angle of view tends to be small, and the angle of view is large for telephoto, making it difficult to obtain a bright optical system.

  For this reason, in this optical system, a lens of negative power is disposed closest to the image plane side so that a large image circle can be obtained with respect to the lens diameter on the image plane side. On the other hand, when a lens of negative power is disposed on the image plane side, the incident angle of the off-axis ray input to the image plane, that is, the imaging element becomes too large (the incident ray angle rises) It tends to be insufficient or the aberration correction is insufficient. Therefore, in this optical system, a lens of a positive power (diaphragm side lens) on the most object side of the third lens group, that is, on the side of the most aperture stop (hereinafter may be referred to as the stop), In order to satisfy the above condition (1), the aperture stop is disposed near the aperture stop so as to suppress the divergence of the light from the aperture stop, particularly the off-axis light with respect to the optical axis. As a result, the angle of the light beam incident on the image plane can be reduced (spreaded), and the above-mentioned problems can be suppressed.

  In addition, since the spread of the light beam on the image plane side from the aperture stop can be suppressed, and the increase in the lens diameter on the image plane side with respect to the image circle can be suppressed, the lens on the object side with respect to the lens diameter on the image plane side It can suppress that a diameter becomes large. Also, by making the surface of the positive power lens (the surface on the most stop side of the third lens group) suitable for focusing on the most object side of the third lens group close to the aperture stop, the peripheral light is made third It is easy to take in the lens group of the lens, and it is possible to suppress the reduction of the angle of view. Therefore, it is possible to provide an optical system in which the lens diameter on the most object side of the optical system is small and the angle of view is large.

  When the value exceeds the upper limit of the condition (1), the surface closest to the object side of the third lens group (the object side (stop side) surface of the stop side lens) is too far from the aperture stop, and the diameter of the image plane side lens is It becomes difficult to suppress the increase and to obtain a compact optical system. When the value goes below the lower limit of the condition (1), the object-side surface of the stop-side lens gets too close to the aperture stop, so the ratio of the upper and lower light fluxes (light flux) to the stop changes and aberration correction becomes difficult . The lower limit of the condition (1) may be 0.15, and aberration correction becomes easier. The upper limit may be 0.25, and the increase in the diameter of the image plane side lens can be further suppressed.

It is desirable that the combined focal length f2 of the second lens group and the focal length fs of the stop side lens satisfy the following condition (2).
0.1 <| f2 / fs | <0.8 (2)
When the value exceeds the upper limit of the condition (2), the power of the aperture stop lens becomes too large with respect to the power of the second lens group that performs focusing, which makes aberration correction difficult. On the other hand, when the value goes below the lower limit of the condition (2), the power of the stop side lens is too weak, which makes it difficult to control the ray angle with respect to the image plane. The lower limit of the condition (2) may be 0.3, which makes it easier to control the ray angle with respect to the image plane. The upper limit may be 0.6, which makes aberration correction easier.

The focal length f1 of the first lens group, the focal length f2 of the second lens group, and the back focus BF may satisfy the following conditions (3) and (4). The back focus BF is a back focus length of this optical system (lens system) when focusing on an infinite distance object.
-10 <f2 / BF <-1.4 (3)
−1.5 <f2 / f1 <−0.7 (4)
If the upper limits of the conditions (3) and (4) are exceeded, the power of the second lens unit is too strong, and aberration correction becomes excessive. Below the lower limits of the conditions (3) and (4), the power of the second lens unit is too weak to be effective in focusing, the moving distance becomes long, and the lens length becomes long. The lower limit of the condition (3) may be -4, and the lower limit of the condition (4) may be -1.3. The lens length can be further suppressed from increasing. The upper limit of the condition (4) may be −0.8, which can suppress excessive aberration correction.

The third lens group can be composed of a stop side lens arranged in order from the object side, a lens of positive refractive power, a biconcave negative lens, and an image plane side lens. It is desirable that the curvature radius RLN2 of the image side surface of the biconcave negative lens and the back focus BF satisfy the following condition (5).
0.05 <BF / RLN2 <0.5 (5)
When the value exceeds the upper limit of the condition (5), the absolute value of the curvature becomes large, the power becomes too strong, and it becomes difficult to balance the aberration correction. Also, the back focus BF becomes too short. When the value goes below the lower limit of the condition (5), the power becomes too weak to make aberration correction difficult, and the back focus BF becomes too long. The upper limit of the condition (5) may be 0.4, which makes it easy to balance aberration correction.

The lens closest to the image plane may be a negative meniscus lens convex on the image plane side, and the radius of curvature RLL1 of the surface on the object side of the lens on the image plane side and the radius of curvature RLN2 satisfy the following condition (6) May be satisfied. A compact optical system with a large image circle can be provided.
-1.0 <(RLL1 + RLN2) / (RLL1-RLN2) <-0.1
... (6)
When the value exceeds the upper limit of the condition (6), the power of the combination of the facing surfaces of the last two lenses on the image plane side becomes too large, and the back focus BF becomes too short. On the other hand, when the value goes below the lower limit of the condition (6), the power of the combination of the facing surfaces is insufficient, the back focus BF becomes too long, and the lens diameter and the lens length become large. The upper limit of the condition (6) may be −0.5, which can further suppress the back focus BF from being too short.

In this optical system, in the telephoto type, the lens diameter on the object side can be made smaller than the lens diameter on the image plane side. For example, the effective diameter De1 of the object side surface of the lens closest to the object side in the first lens group and the effective diameter DeLL2 of the surface close to the image plane side of the third lens unit on the image side are as follows. You may satisfy (7).
0.9 <De1 / DeLL2 <1.0 (7)

In this optical system, it is possible to shorten the total length LA of the optical system as a telephoto type, and the total length LA and the back focus BF may satisfy the following condition (8).
1.5 <LA / BF <5.0 (8)
The lower limit of the condition (8) may be 2.0 and the upper limit may be 4.0.

Furthermore, in this optical system, the effective diameter De1 of the object side surface of the lens closest to the object side in the telephoto type can be smaller than the back focus BF, and the following condition (9) may be satisfied.
0.8 <De1 / BF <2.0 (9)
The upper limit of the condition (9) may be 1.6.

  One of the other aspects of this invention is an imaging device which has said optical system and the image pick-up element arrange | positioned at the image surface side of an optical system. The optical system may be a replacement lens, and the imaging device includes a digital camera, a video camera, a TV camera, and an action camera. Since a large-diameter and compact optical system can be provided, the imaging apparatus can be miniaturized.

BRIEF DESCRIPTION OF THE DRAWINGS The figure which shows the outline | summary of the imaging device containing the optical system for imaging. FIG. 2 is a view showing lens data of the optical system shown in FIG. 1; FIG. 2 is a view showing a focal length of the optical system shown in FIG. FIG. 2 shows various aberrations of the optical system shown in FIG. FIG. 2 shows transverse aberration of the optical system shown in FIG. FIG. 1 is a schematic view of an imaging apparatus including different optical systems for imaging. FIG. 7 is a view showing lens data of the optical system shown in FIG. 6; FIG. 7 shows the focal length of the optical system shown in FIG. FIG. 7 shows various aberrations of the optical system shown in FIG. 6; FIG. 7 shows transverse aberration of the optical system shown in FIG. 6;

  FIG. 1 shows an example of an imaging apparatus (camera, camera apparatus) provided with an optical system for imaging. The camera 1 is disposed on an optical system (imaging optical system, imaging optical system, lens system) 10 and an image plane side (imaging side, image forming side) 12 of the optical system 10 to form an image plane 5a. And an element (imaging device) 5. The optical system 10 includes, in order from the object side 11 to the image plane 5a, a first lens group G1 of generally positive refractive power, a second lens group G2 of generally negative refractive power, and an aperture stop It is composed of St and a third lens group G3 having a positive refractive power as a whole, and the first lens group G1, the aperture stop St and the third lens group G3 are fixed to the image plane 5a during focusing. The second lens group G2 is an optical system 10 for imaging of the inner focus type in which the second lens group G2 moves relative to the image plane 5a.

  The first lens group G1 has a four-lens configuration, and is disposed in order from the object side 11 along the optical axis 15, and has a positive refractive power convex to the object side 11 (power, hereinafter, the refractive power is simply positive or Negative lens), a positive meniscus lens L2 convex on the object side 11, a negative meniscus lens L3 convex on the object side 11, and a positive meniscus lens L4 convex on the object side 11. And consists of The positive meniscus lens L2 and the negative meniscus lens L3 constitute a cemented lens B1 of negative refractive power. That is, the first lens group G1 has a positive-positive-negative-positive or positive-negative-positive power arrangement.

  The second lens group G2 has a two-lens configuration, and includes a positive meniscus lens L5 convex on the image plane side 12 and a biconcave negative lens L6, which are sequentially arranged from the object side 11 along the optical axis 15 These lenses L5 and L6 constitute a cemented lens B2 of negative refractive power. The cemented lens B2 moves back and forth along the optical axis 15 for focusing.

  The third lens group G3 disposed on the image plane side 12 across the aperture stop St relative to the second lens group G2 has a four-lens configuration, and is disposed in order from the object side 11 along the optical axis 15, A positive meniscus lens (diaphragm side lens) L7 convex on the object side 11, a biconvex positive lens L8, a biconcave negative lens L9, and a lens element disposed most on the image plane side 12 and convex on the image plane side 12 And a negative meniscus lens (image side lens) L10. That is, the third lens group G3 has a positive-positive-negative-negative power arrangement. Therefore, this optical system is a 10-piece configuration including two cemented lenses in total, and the object side 11 is positive-negative-positive-negative (in lens units, positive-positive-negative-) with the aperture stop St interposed. Positive-positive-negative), the image plane side 12 has positive-positive-negative-negative power arrangement, and the combination of telephoto power of the plus lead has a power arrangement which has a compact configuration as a whole.

  The data of each lens which comprises the optical system 10 in FIG. 2 are shown. The radius of curvature (R) is the radius of curvature (mm) of each surface of each lens arranged in order from the object side 11, the distance d is the distance between each lens surface (mm), and the effective diameter De is the effective diameter of each lens surface ( The diameter, mm) and the refractive index nd indicate the refractive index (d line) of each lens, and the Abbe number 数 d indicates the Abbe number (d line) of each lens. Note that d19 indicates the distance (back focus, BF) between the optical system 10 and the imaging device 5. FIG. 3 shows the focal length (mm) on the d-line basis of each lens, the combined focal length (mm) of each cemented lens B1 and B2, and the combined focal length (mm) of each lens group G1 to G3. ing. The same applies to lens data shown below. Also, the focal length described below is a d-line reference value.

  FIG. 4 shows spherical aberration, astigmatism, and distortion of the optical system 10. The spherical aberration has a wavelength of 435.8340 nm (two-dot chain line), a wavelength of 486.1330 nm (long broken line), a wavelength of 546.0740 nm (solid line), a wavelength of 587.5620 nm (one-dot chain line), and a 656.2730 nm (short dashed line). And show. Astigmatism indicates tangential ray T and sagittal ray S. FIG. 5 shows the chromatic aberration of magnification (lateral aberration) of the optical system 10 for each of the tangential ray and the sagittal ray at the above-mentioned respective wavelengths. The same applies to the aberration diagrams shown below.

The numerical values indicating the main performance of this optical system 10 are as follows.
Overall synthetic focal length (f): 89.94 mm
F value: 3.26
Maximum angle of view (half angle of view): 17.46 degrees Image circle: φ 56 mm
Back focus (BF): 24.02 mm
Overall lens length (LA): 80.29 mm

The values of the conditions (1) to (9) of the optical system 10 are as follows, and all the conditions are satisfied. The inside of the brackets indicates the corresponding parameters of the optical system 10 of this example.
Condition (1) (dS / dI, “d11 / (d12 to d19)”): 0.207
Condition (2) (| f2 / fs |, “| f2 / fL7 |”): 0.361
Condition (3) (f2 / BF): -2.35
Condition (4) (f2 / f1): -0.937
Condition (5) (BF / RLN2, "BF / R17"): 0.102
Condition (6) ((RLL1 + RLN2) / (RLL1-RLN2),
"(R18 + R17) / (R18-R17)": -0.799
Condition (7) (De1 / DeLL2, “De1 / De19”): 0.99
Condition (8) (LA / BF): 3.34
Condition (9) (De1 / BF): 1.50

  The imaging optical system 10 includes, from an object side 11, a first lens group G1 of positive power, a second lens group G2 of negative power, an aperture stop St, and a third lens group G3 of positive power. , An optical system close to a telephoto type (telephoto type, reverse retro focus type) having positive-negative-positive power arrangement, and an inner focus type in which the second lens group G2 is moved during focal length adjustment (focusing) Optical system. This telephoto type optical system can generally increase the focal length, but the angle of view is small, and if it is attempted to secure the angle of view, the effective diameter of the object side 11 increases. Therefore, if the effective diameter of the lens on the image plane side 12 is simply increased by realizing the large image circle of φ 56 mm as described above so as to correspond to the large image pickup device 5, the optical system becomes large and the entire length is also increased. It becomes a long and heavy lens system.

  On the other hand, in the optical system 10, by disposing the lens L10 of negative power on the image plane side 12 most, an image circle having a size larger than the effective diameter of the image plane side lens L10 can be obtained. There is. Further, the surface on the object side of the lens (diaphragm side lens) L7 of positive power so as to satisfy the condition (1) at the most object side 11 of the third lens group G3, that is, the vicinity of the aperture stop St. The most stop side surface S12 of the third lens group G3 is disposed to suppress divergence of light rays from the aperture stop St, particularly off-axis light, with respect to the optical axis 15, and lens L10 of negative power on the image side 12 The incident angle of the off-axis ray input to the image plane 5a, that is, the image pickup device 5 is laid down (smallened) to secure the light amount of the peripheral light and to sufficiently perform the aberration correction. Therefore, the negative lens L10 can be adopted most on the image plane side 12, thereby making it possible to suppress an increase in diameter De19 (DeLL2) of the lens L10 on the image plane side 12 with respect to the image circle. Therefore, the diameter De1 of the lens L1 on the object side 11 can be suppressed from becoming larger than the diameter De19 of the lens L10 on the image plane side 12.

  Further, by bringing the lens L7 of positive power suitable for condensing on the most object side 11 of the third lens group G3 closer to the aperture stop St, ambient light is easily taken into the third lens group G3, and It can control that a corner becomes small. Therefore, the diameter De1 of the lens L1 on the most object side 11 of the optical system 10 is small, and the optical system 10 having a large angle of view can be provided. In this example, it is possible to provide the optical system 10 in which the effective diameter De1 of the lens L1 closest to the object 11 is smaller than the effective diameter De19 of the lens L10 closest to the image plane 12.

  Furthermore, the relationship between the power (focal length f2) of the second lens group G2 that faces the lens L7 via the aperture stop St and performs inner focusing, and the power (focal length fs) of the lens L7 is condition (2) And the power of the stop-side lens L7 of the third lens group G3 can be favorably corrected for aberration, and the light ray angle with respect to the image plane 5a can be appropriately controlled.

  The power (focal length f2) of the second lens group G2 is set to satisfy the conditions (3) and (4) with respect to the back focus BF and the power of the first lens group (focal length f1). The second lens unit G2 can sufficiently perform aberration correction, secures focusing performance, and realizes the optical system 10 with a shorter total length LA. In the optical system 10, the second lens group G2 is driven by a motor at the time of focusing, but the power of the second lens group G2 is set in the range satisfying the conditions (3) and (4). As a result, the second lens group G2 is formed of a two-lens configuration of the lenses L5 and L6, specifically, only the cemented lens B2, and the optical system 10 is lightweight and has a small motor load.

  The third lens group G3 includes, in order from the object side 11, lenses L7 and L8 of positive power and lenses L9 and L10 of negative power. The lens L9 and the lens L10 of the optical power of 10% are used to suppress the lens diameter on the image plane side 12 so that a large image circle can be formed. In particular, by setting the second lens L9 on the image plane side 12 as a biconcave negative lens and setting the curvature radius R17 of the surface on the image plane side 12 to the range of the condition (5), the light is incident on the image plane 5a. It is possible to suppress that the ray angle becomes too large, and to make it possible to form a clearer image. The back focus BF is not too long.

  The image plane side lens L10 closest to the image plane is a negative meniscus lens convex on the image plane side 12, and the last two lenses L10 and L9 on the image plane side 12 face each other to satisfy the condition (6) It forms a combination of faces. These surfaces ensure negative power and secure the number of surfaces required for aberration correction, and can also suppress an increase in curvature of field due to the Petzval sum becoming too large.

  Therefore, the optical system 10 can make the diameter De1 of the lens L1 on the object side 11 smaller than the diameter De19 of the lens L10 on the image side 12 as a telephoto type, and in the present example, the lens L1 of the most object side 11 The optical system 10 is smaller than the lens L10 on the image plane side 12 most. In addition, although the image circle is as large as φ56 mm, a relatively long back focus BF can be secured, and the lens L1 on the most object side 11 is smaller than the back focus BF, and the overall length LA is short. (Optical system) 10 is provided. Further, the optical system 10 is suitable as an interchangeable lens or the like, which has a large angle of view of 17.46 degrees in half angle of view as a telephoto type, and a F number of 3.26.

  FIG. 6 shows an example of a camera 1 provided with optical systems 10 for different imaging. This optical system 10 also has, in order from the object side 11 to the image plane 5a, a first lens group G1 of positive refractive power as a whole, a second lens group G2 of negative refractive power as a whole, and an aperture The inner-focus type imaging optical system 10 includes the aperture stop St and a third lens unit G3 having a positive refractive power as a whole, and the second lens unit G2 moves during focusing. The first lens group G1 has a four-lens configuration, the second lens group G2 has a two-lens configuration, and the third lens group G3 has a four-lens configuration. The basic lens configuration of each group is common to the above-described optical system, and thus the description thereof is omitted, but the optical system is a ten-lens configuration including two sets of cemented lenses B1 and B2.

  The data of each lens which comprises the optical system 10 in FIG. 7 is shown. FIG. 8 shows the focal length (mm) on the d-line basis of each lens and the combined focal length (mm) of each lens group. FIG. 9 shows the spherical aberration, astigmatism and distortion of the optical system 10, and FIG. 10 shows the chromatic aberration of magnification (lateral aberration) of the optical system 10 for each of the tangential and sagittal rays at the above-mentioned respective wavelengths. It shows.

The numerical values indicating the main performance of this optical system 10 are as follows.
Overall synthetic focal length (f): 95.19 mm
F value: 3.4
Maximum angle of view (half angle of view): 16.55 degrees Image circle: φ 56 mm
Back focus (BF): 34.05 mm
Overall lens length (LA): 72.46 mm

The values of the conditions (1) to (9) of the optical system 10 are as follows, and all the conditions are satisfied. The inside of the brackets indicates the corresponding parameters of the optical system 10 of this example.
Condition (1) (dS / dI, “d11 / (d12 to d19)”): 0.200
Condition (2) (| f2 / fs |, “| f2 / fL7 |”): 0.345
Condition (3) (f2 / BF): −1.60
Condition (4) (f2 / f1): -0.917
Condition (5) (BF / RLN2, "BF / R17"): 0.300
Condition (6) ((RLL1 + RLN2) / (RLL1-RLN2),
"(R18 + R17) / (R18-R17)":-0.662
Condition (7) (De1 / DeLL2, “De1 / De19”): 0.97
Condition (8) (LA / BF): 2.13
Condition (9) (De1 / BF): 0.88

  As described above, the optical system (lens system) 10 disclosed above relates to an imaging optical device and a digital device, and is applicable to a lens-interchangeable digital camera, a video camera, a TV camera, an action camera, etc. A suitable large aperture compact optical system 10. In particular, it is suitable as a lens system with a large image circle to be used for a large image pickup device 5, and has a performance as a telephoto lens while having a simple configuration of 10 pieces, 3 groups, and further a long back focus BF Accordingly, it is possible to provide an optical system 10 which has a small lens diameter and a total lens length LA, is wide-angle and bright, and is well corrected for aberration.

In the above, in order from the object side to the image plane, the first lens group having a positive refractive power as a whole, the second lens group having a negative refractive power as a whole, and the aperture stop as a whole And a third lens group having a refractive power of, and the third lens group is a lens of positive refractive power disposed closest to the object side and a negative lens disposed closest to the image plane side The distance dS between the surface on the object side of the stop side lens and the aperture stop and the distance dI between the surface on the object side of the stop side lens and the image plane An optical system satisfying the following conditions is disclosed. In addition, an imaging apparatus is disclosed that includes these optical systems and an imaging device disposed on the image side of the optical system.
0.02 <dS / dI <0.3

In this optical system, during focusing, the first lens group, the aperture stop and the third lens group are fixed to the image plane, and the second lens group is fixed to the image plane. You may move. The combined focal length f2 of the second lens group and the focal length fs of the diaphragm side lens may satisfy the following conditions.
0.1 <| f2 / fs | <0.8

The focal length f1 of the first lens group, the focal length f2 of the second lens group, and the back focus BF may satisfy the following conditions.
-10 <f2 / BF <-1.4
−1.5 <f2 / f1 <−0.7

The third lens group is composed of the diaphragm side lens arranged in order from the object side, a lens of positive refractive power, a biconcave negative lens, and the image plane side lens. The radius of curvature RLN2 of the surface on the image plane side of the concave negative lens and the back focus BF may satisfy the following conditions.
0.05 <BF / RLN2 <0.5

The image plane side lens may be a negative meniscus lens convex on the image plane side, and the curvature radius RLL1 of the object side surface of the image plane side lens and the curvature radius RLN2 may satisfy the following conditions.
-1.0 <(RLL1 + RLN2) / (RLL1-RLN2) <-0.1

The effective diameter De1 of the object side surface of the lens closest to the object side of the first lens group and the effective diameter DeLL2 of the surface of the image side lens on the image side may satisfy the following conditions.
0.9 <De1 / DeLL2 <1.0

The total length LA and the back focus BF of the optical system may satisfy the following conditions.
1.5 <LA / BF <5.0

The effective diameter De1 of the object-side surface of the lens closest to the object in the first lens group and the back focus BF may satisfy the following conditions.
0.8 <De1 / BF <2.0

10 optical system, G1 first lens group, G2 second lens group, G3 third lens group

Claims (10)

In order from the object side to the image plane, a first lens group of generally positive refractive power, a second lens group of generally negative refractive power, an aperture stop, and generally of positive refractive power It consists of the third lens group,
At the time of focusing, the first lens group, the aperture stop, and the third lens group are fixed with respect to the image plane, and the second lens group is moved with respect to the image plane. The lens group of the lens has a positive refractive power, which is disposed closest to the object side, a lens with positive refractive power, a biconcave negative lens, and a negative refractive power that is disposed most toward the image plane. An optical system constituted by an image plane side lens. In claim 1,
An optical system in which a distance dS between a surface on the object side of the diaphragm side lens and the aperture stop and a distance dI between a surface on the object side of the diaphragm side lens and the image plane satisfy the following condition.
0.02 <dS / dI <0.3 In claim 1 or 2,
An optical system in which a combined focal length f2 of the second lens group and a focal length fs of the aperture stop-side lens satisfy the following conditions.
0.1 <| f2 / fs | <0.8 In any of claims 1 or 3,
An optical system in which a focal length f1 of the first lens group, a focal length f2 of the second lens group, and a back focus BF satisfy the following conditions.
-10 <f2 / BF <-1.4
−1.5 <f2 / f1 <−0.7 In any one of claims 1 to 4,
An optical system in which a curvature radius RLN2 of a surface on the image plane side of the biconcave negative lens and a back focus BF satisfy the following conditions.
0.05 <BF / RLN2 <0.5 In claim 5,
The optical system, wherein the image plane side lens is a negative meniscus lens convex on the image plane side, and the radius of curvature RLL1 of the surface on the object side of the image plane side lens and the radius of curvature RLN2 satisfy the following conditions.
-1.0 <(RLL1 + RLN2) / (RLL1-RLN2) <-0.1 In any one of claims 1 to 6,
An optical system in which an effective diameter De1 of an object side surface of a lens closest to the object side of the first lens group and an effective diameter DeLL2 of an image surface side surface of the image surface side lens satisfy the following condition.
0.9 <De1 / DeLL2 <1.0 In any one of claims 1 to 7,
An optical system in which the total length LA and the back focus BF of the optical system satisfy the following conditions.
1.5 <LA / BF <5.0 In any one of claims 1 to 8,
An optical system in which an effective diameter De1 of an object side surface of a lens closest to the object side in the first lens group and a back focus BF satisfy the following condition.
0.8 <De1 / BF <2.0 An optical system according to any one of claims 1 to 9,
And an imaging device disposed on the image side of the optical system.

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